Mar 21 2022

Origins of Life From RNA

Published by under Evolution
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It is common to observe that one of the greatest unsolved questions of science is how life began. This is a distinct question from how the diversity of the species of living things emerged. It is well established that once life had established a self-replicating system capable of generating some variation, that evolutionary forces would kick in and could, and in fact did, create all life on Earth. But we are a long way from reverse-engineering in any detail how those first organic molecules transitioned from chemistry to life.

This is not a scientific question that will be meaningfully resolved with a single experiment or discovery. Answers will slowly yield over time, as they already are, and it will take decades and perhaps centuries for something approaching a complete picture to emerge. But this progress will be built one study at a time, and Japanese scientists have recently contributing a significant piece to the puzzle.

Researchers at the University of Tokyo published a study in Nature Communications in which they establish that an RNA system can spontaneously evolve complexity. RNA molecules are one of the primary candidates for the first prebiotic molecules that lead to life. RNA is a single-stranded version of DNA, a self-replicating molecule built from four bases forming two pairs. The idea is that life started with the formation of a “replicator” – a molecule that could make copies of itself. RNA is a leading candidate for being the first replicator, but DNA and proteins are also candidates. So far we have not yet been able to connect an “RNA world” with a later world comprised of DNA and proteins. It is this gap that the new research helps fill in.

The real challenge is creating a system of one or more replicators that is capable of undergoing Darwinian evolution. That’s the key. Once you have a self-sustaining system that can not only replicate but generate variation and be subject to adaptive pressures so that evolution can take place, then life has a foothold and can take off from there. The researchers started with an RNA molecule that was able to replicate with a self-coded RNA replicase. They found:

The RNA diversifies into multiple coexisting host and parasite lineages, whose frequencies in the population initially fluctuate and gradually stabilize. The final population, comprising five RNA lineages, forms a replicator network with diverse interactions, including cooperation to help the replication of all other members.

This is highly significant. It answers at least one important question – could different RNA populations co-exist? The concern was that if different RNA populations are all competing for the same resources, then only one would predominate in the end. But in this experiment five different RNA populations happily coexisted, and even “cooperated” for mutual benefit.

This RNA network had the critical components of evolutions – able to generate new information, greater complexity, and new variation. Further there was a differential survival of those molecules better able to function in the network in order to self-replicate. This is, in short, evolution. Give it a few billion years and you might have something interesting.

Does this mean this is how life emerged? No, this type of laboratory research by itself will not be able to determine that. We cannot go back in time to see what happed on the early Earth. If, at some point, we can travel to other worlds which happen to be at various stages of the early evolution of life then we may be able to make direct observations of how such a process unfolds. But until then, we can only conduct proof-of-concept experiments to determine what is possible. That is what this experiment does. It shows it is possible for RNA to form into not only a self-replicating system, but an evolving system, out of which greater complexity can emerge. This is a critical step in bootstrapping to a living system.

There are still many steps between this RNA network and a living cell. We still need to get from RNA to a complex system in which DNA directs the translation of proteins which in turn regulate the replication of the DNA. Bubbles of two lipid layers spontaneously form, but how did the DNA-protein system contain itself inside these bilipid bubbles? Once they do it’s easy to see how proteins would evolve to modify those membranes and their function. At this point we basically have single-celled life.

The authors acknowledge that it’s possible an RNA network such as the one they produced could have emerged in the early “primordial soup” but that this was a dead-end and did not lead to life. Other replicators may have been the actual pathway leading to life on Earth. There is a lot of research ahead, probing many possible pathways that connect the dots from chemical to living systems. But the pieces are slowly falling into place.

I also suspect that computer simulations will increasingly play a role in this research. As supercomputers and AI algorithms get more powerful it is easier to imagine a computer simulation that can run through millions of years of evolution to see what kinds of things can happen. We may need to wait for mature quantum computers before truly powerful simulations can be done. But eventually we will likely be able to evolve virtual life “in silico” and this may turn out to be the most powerful evidence we can develop to determine how life on Earth likely arose.

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